The invention relates to a method and a system preparing samples for gas chromatography.
In order to prepare samples for gas chromatography, it is known to connect a liquid chromatograph (LC) upstream of the gas chromatograph (GC). For this purpose, in on-line operation, a valve circuit with fixed bypass injector is used. Immediately after passing an LC detector, the sample material is removed from the LC and conveyed via a transfer line to a complicated valve device which is connected in such a way that the sample material contained in the bypass injector is flushed directly into a gas-chromatography capillary column using a carrier gas. However, such columns have only a limited sample capacity, so that this operation is possible only by employing complicated coupled-column technique comprising up to three series-connected capillary columns, firstly a gas-chromatographically inactive column for holding the sample material, then a precolumn for blending out the solvent, and finally a main column for the chromatographic separation. A so-called early-vapor exit is situated between the latter two columns. In this case, the bypass injector can only be changed by means of costly modification of the device. There are not possibilities for variation, and only the start of feed to the inactive column, and hence the selection of the starting point of a chromatographic region of interest, can be influenced.
In off-line operation, the sample material, downstream of the LC, is in sample bottles of a fraction collector, in order then to be analyzed further in a conventional manner.
The object of the invention is to provide a method and a system for preparing samples for gas chromatography, the sample material being guided through a liquid chromatograph by means of a solvent and being monitored by means of a detector, and, on the basis of the detector recognizing a chromatographic region of interest, the sample material of this region being removed from the stream leaving the liquid chromatograph and being analyzed by gas chromatography, characterized in that the stream of sample material leaving the liquid chromatograph is guided through a flow-through cuvette, and the removal is carried out, until the end of the chromatographic region of interest, via a syringe, which is introduced into a flow-through cuvette and is drawn upwards at a predetermined ratio to the transport rate of the stream when that region of the sample material which is of interest has reached the flow-through cuvette.
A feature of the invention is that it allows simple and variable preparation of samples.
As a result, the quantity of sample material which can be used for gas chromatographic analysis is variable and not constant. The removal of the sample material which is to be analyzed by gas chromatography is both very simple and the apparatus is simple.
Further configurations of the invention can be found in the following description and the subclaims.
The invention is explained in more detail below with reference to exemplary embodiments which are illustrated in the appended drawings, in which: